The field of the present invention is radial flow turbines and more specifically variable primary nozzle systems in radial flow turbines.
Radial turbines employ an annular inlet surrounding a turbine wheel through which is directed influent under pressure. To uniformly distribute the influent, primary, stationary vanes are disposed about the annular inlet to create nozzles therebetween. These nozzles are often variable through the controlled pivotal motion of the primary vanes.
The primary vanes are typically mounted between mounting rings. One of the mounting rings may be pivotally mounted relative to the other mounting ring which is then employed as a means for pivoting the vanes. The mounting rings are also mounted for relative axial movement therebetween. Normally, one ring is fixed while the other is allowed to move axially to accomplish this result. A pneumatic or hydraulic cylinder is associated with the pivotal mounting ring to forcefully control the position of the ring, in turn controlling the vanes.
Because of the inherent pressures in such radial turbines, particularly the static and dynamic pressures of the flow through the primary nozzles, clamping forces are applied by the mounting rings to the sides of the vanes adjacent the mounting rings if one or both of the rings is axially movable. The close fit of the rings about the vanes prevents leakage flow bypassing the nozzles. However, the resulting clamping forces often can become excessive and actuation of the vanes to adjust the nozzles is inhibited.
Two earlier methods of attempting to control clamping forces are disclosed in U.S. Pat. Nos. 3,495,921 and 4,300,869, both issued to Judson S. Swearingen, the disclosures of which are incorporated herein by reference. In U.S. Pat. No. 3,495,921, a step-cut in the clamping surfaces is employed such that the inlet pressure extends to a point inwardly of the outer extent on the nozzle blades. In this way the static inlet pressure will resist the reduced pressure in the nozzles over a larger area of the mounting rings. In U.S. Pat. No. 4,300,869, cavities are fixed to the sides of the vanes adjacent the mounting rings. These cavities include passages which extend to a source of either vacuum or pressure to affect the axial clamping forces of the rings. In the latter patent, the effect of the cavities largely results from the orientation of the vanes.